Abstract Detail

Differential Performance of Four Pines in Relation to Elevational Position in the San Bernardino Mountains, California.

The distribution patterns of trees across moisture gradients in the western United States reflect speciesí abilities to tolerate internal water deficits. In an effort to elucidate the ecophysiological mechanisms responsible for the stratification of pines across the elevational gradient of the San Bernardino Mountains in southern California, we measured a suite of tree physiological responses (relative water content, spectral reflectance, transpiration decline) and needle morphology characteristics (leaf mass per unit area). Mature trees of four species were included in the study that were distributed in order from low to high elevation including: Pinus attenuata , P. coulteri , P. lambertiana , and P. contorta . Plant water relations and needle morphology measurements were significantly correlated. Needle relative water content and leaf mass per unit area were significantly higher for P. lambertiana and P. contorta . Stomatal and cuticular transpiration was also higher for high elevation species. The low elevation and high elevation species had similar reflectance spectra, suggesting that harsh growing conditions may pervade at both low and high elevations. Results from this study suggest that southern California pine distributions are heavily influenced by speciesí adaptations for tolerating moisture stress, but that other factors such as light may also influence tree dominance patterns.